Generally, a resolver is a kind of sensor for measuring a rotation angle and a rotation speed of a rotating device such as a motor. Recently, the resolver is widely used in various technical fields, particularly to a high-precision control system such as an electric power steering system which demands measurement and control of a rotation angle and a rotation speed with high precision. Therefore, it is needed to accurately figure out and analyze various factors giving an influence on the measurement performance of the resolver and reflect these factors on the design of the resolver in order to minimize a measurement error of the resolver and improve the measurement precision to the maximum.
However, in existing techniques, it is just intended to improve the measurement performance by changing configurations of an excitation coil and an output coil disposed at a stator of a resolver as disclosed in Japanese Unexamined Patent Publication No. 1996-178611, or it is just intended to improve the measurement performance by changing a shape of a rotor of a resolver as disclosed in Japanese Unexamined Patent Publication No. 2005-49183, so a width relation between a back yoke of the stator and the rotor is not considered as a factor giving an influence on the measurement performance of the resolver. In other words, if the back yoke of the stator is designed to have a width smaller than a width of the rotor over a certain level, a magnetic flux of the stator is overcrowded excessively, or a magnetic saturation is generated to disturb a flow of the magnetic flux, thereby deteriorating the measurement performance of the resolver. However, in existing techniques, this drawback is not reflected on the design of the resolver.
Further, in existing techniques, it is not proposed to optimize a relation between a width of the stator and a width of the back yoke of the rotor and reflect the relation on the design of the resolver to facilitate a resolver designing work.